1. Field of the Invention
The invention relates to an image forming apparatus with an electrode unit having a plurality of apertures for use in a copying machine, a printer, a plotter, a facsimile machine, or other apparatus having a printing function.
2. Description of the Related Art
Heretofore, there has been conventionally proposed an image forming apparatus in which an image is formed using a plurality of apertures. In this image forming apparatus, a voltage is selectively applied to the apertures in accordance with image data to control toner particles to selectively pass through the apertures. The toner particles which pass through the apertures form an image on an image forming medium. This type of an image forming apparatus is disclosed in the U.S. Pat. No. 3,689,935.
The image forming apparatus includes an aperture electrode having a plain plate made of an insulating material, a continuous reference electrode formed on a one side of the plain plate and a segmented control electrode formed on the other side of the plain plate. Control electrodes of the segmented control electrode are insulated from each other and the aperture electrode is formed as at least one row of apertures through the three layers including each control electrode of the segmented control electrode. The image forming apparatus further comprises a power supply for selectively supplying an electric potential between the reference electrode and the segmented control electrode, a toner supplier for supplying toner particles so that the density of the particle stream is modulated according to the pattern of the potentials applied to the control electrodes of the segmented control electrode, and positioning means for positioning a print receiving medium in the particle stream by relatively moving the print receiving medium and the aperture electrode.
However, the conventional apparatus does not achieve high speed printing and further has a reduced printing quality due to blinding of the apertures.
The applicant proposed an improved apparatus of this image forming apparatus in the U.S. patent application Ser. No. 08/112,471, filed on Aug. 28, 1993. The apparatus of the application improves the printing characteristic by contacting an aperture electrode with a toner carry means carrying the toner. In the apparatus, toner particles are supplied concurrently with contacting the toner around the apertures of the aperture electrode so that toner which causes the blinding of the apertures doesn't accumulate in the apertures. Consequently the apertures of the aperture electrode aren't blinded.
In the apparatus of the application, the toner particles are attached to toner carrier means by image-force or Van der Waals force. To detach the toner particles from the toner carrier means and pass the toner particles through the apertures during a printing operation, a high driving voltage is required. Therefore, the printing apparatus, including a driving element with a high output voltage, becomes expensive.